1. Field of the Invention
The present invention relates to a video endoscope apparatus employing a device shutter capable of preventing the occurrence of blurred images.
2. Description of the Related Art
In recent years, an electronic type of endoscope (such as an electronic scope) employing imaging means constituted by a solid state imaging device such as a charge coupled device (hereinafter referred to as the "CCD") has been used in practice.
Such an electronic scope has the advantage that recording and reproduction of images can be readily performed compared with those of an optical type of scope.
In a generally used method of driving a CCD, as is known, charges are stored (integrated) in each of photodiodes which constitute the CCD for approximately 1/60 seconds, and the thus-stored charges are read from the CCD at time intervals of 1/60 seconds to provide video signals. As a matter of course, if an object moves during the 1/60-second period required for charges to be stored, the obtained video signals become remarkably low in resolution, that is, the obtained image is blurred.
In the field of television cameras for home use, a so-called device shutter function is utilized to eliminate the above-described problem of blurred images. The device shutter is an electrical means for shortening the storage time so that a conventional storage time of 1/60 seconds (in a frame storage system, 1/30 seconds) is reduced to, for example, 1/600 seconds equivalent to one tenth of 1/60 seconds.
Japanese Patent Laid-open No. 121779/1980 discloses an endoscopic imaging apparatus arranged to store charges for one frame period or a plurality of frame periods in a television receiver whose frame period is fixed.
In this related art example, if an object to be imaged is moving, imaging (storage of charges) is performed for one frame period, while, if the quantity of light is insufficient, storage of charges is performed over a plurality of frame periods, whereby images which are high in S/N ratio can be obtained.
However, even this related art example cannot eliminate any blurred image which may occur within one frame period.